Process for manufacturing polyarylene sulfide

Abstract: A process for efficiently manufacturing high purity polyarylene sulfide. The process comprises feeding a liquid or gaseous sulfur compound (e.g. hydrogen sulfide) to a mixture comprising lithium hydroxide and a non-lithium hydroxide solid compound (e.g. alkali metal chloride or alkaline earth metal chloride) in a non-protonic organic solvent (e.g. N-methyl-2-pyrrolidone), separating the alkali metal chloride or alkaline earth metal chloride, adjusting the sulfur content of the reaction mixture, feeding a dihalogeno aromatic compound (e.g. p-dichlorobenzene) to effect a polycondensation reaction, and adding of an alkali metal hydroxide (e.g. sodium hydroxide) to recover lithium ion.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a process for manufacturing polyarylene sulfide, and, more particularly, to a process for manufacturing high quality polyarylene sulfide, useful as a material for electrical or electronic parts and appliances and as a high rigidity material, at a low cost. The present invention further relates to a process for separating a solid compound other than lithium hydroxide (such a solid compound is hereinafter referred to as non-lithium hydroxide solid compound), and, in particular, to a process for efficiently separating a non-lithium hydroxide solid compound produced in the process for manufacturing polyarylene sulfide. Furthermore, the present invention relates to a process for recovering lithium ion, and, in particular, to a process for efficiently recovering lithium ion from a reaction mixture of polyarylene sulfide containing lithium chloride in the process for manufacturing polyarylene sulfide. Description of the Background Art Polyarylene sulfide resins (PAS resins), in particular, polyphenylene sulfide resins (PPS resins), are known as engineering plastics having excellent mechanical strength, heat resistance, and especially high rigidity. They are useful materials for electrical and electronic parts and appliances, and as high rigidity materials for various applications. A conventional process for manufacturing these resins is reacting a dihaloaromatic compound such as p-dichlorobenzene and a sodium salt such as sodium sulfide in an aprotic organic solvent such as N-methyl-2-pyrrolidone (hereinafter abbreviated from time to time as NMP). A problem in this process resides in the difficulty in removing by-produced sodium chloride from resins by washing, since sodium chloride is insoluble in the solvents such as NMP and is incorporated in the resins. A process using a lithium salt instead of the sodium salt is attracting attention as a process for overcoming this problem. Because lithium chloride produced as a side product in the polymerization reaction is soluble in many of the aprotic organic solvents such as NMP, it is possible to comparatively easily reduce the lithium content in the resin. In order to reduce the manufacturing cost of the resins, however, it is essential to recover and reuse lithium which is far more expensive than sodium. As a process for manufacturing polyarylene sulfide resins, including polyphenylene sulfide resins, using the lithium salt, USP 4,451,643 discloses a batch or continuous process for manufacturing these resins by reacting lithium N-methylaminobutyrate (hereinafter abbreviated from time to time as LMAB), produced by the reaction of lithium hydroxide and NMP, a dihaloaromatic compound, such as p-dichlorobenzene, and hydrogen sulfide. In this process, polymers such as PPS resins are synthesized using LMAB, which is a lithium salt but not a sodium salt, as a polymerization raw material, whereby lithium chloride which is soluble in NMP solvent is produced as a side product. Because of this, the amount of alkali metal components incorporated in the polymers is greatly reduced as compared with the conventional process wherein sodium chloride which is insoluble in the solvent is produced as a side product. Nevertheless, this process has a drawback in that LMBA must be first produced by the reaction of lithium hydroxide (LiOH·H 2 O) and NMP. Moreover, because this process uses lithium hydroxide as a starting raw material, lithium chloride produced as a side product by the polymerization reaction must be regenerated into lithium hydroxide for recovering and reuse of this compound. As a method for collecting lithium chloride and converting it into lithium hydroxide, USP 4,451,643 proposes a method of washing the reaction products and the polymers with water to collect lithium chloride as an aqueous solution, and reacting the lithium chloride with sodium hydrogen carbonate or subjecting the aqueous solution to electrolysis to convert the lithium chloride into lithium hydroxide. The method of using sodium hydrogen carbonate requires a complicated process wherein lithium chloride is first converted to lithium carbonate and then to lithium hydroxide. The electrolysis is disadvantageous in view of production cost and is not industrially viable. The process proposed by USP 4,451,643 requires a step for producing lithium N-methyl-aminobutyrate from lithium hydroxide and N-methyl-2-pyrrolidone, wherein a large quantity of water is required for preventing a retarded reaction which takes place when the amount of water is small. This is another drawback which makes the process industrially less attractive. Japanese Patent Application Laid-open (kokai) No. 180928/1990 discloses a process for manufacturing high polymeric PAS, wherein a mixture of an organic polar solvent, sodium hydrosulfide hydrate, and alkali metal aminocarboxylate is dehydrated by distillation or the like, and the dehydrated mixture is mixed and reacted with lithium halide and a dihaloaromatic compound. This process was proposed in order to overcome the difficulty in removing crystal water contained in alkali metal sulfide which was used in a process for manufacturing PAS. However, the mixture to be dehydrated in this process is a slurry which involves a problem when it is subjected to continuous distillation while heating. Although there are no problems when the slurry is treated by batch distillation, in the continuous distillation, the mixture is continuously sent to a distillation column whereby components are separated by boiling point differences among them, removing vapor from the top. Solid components in the slurry may stay and accumulate in column trays, choke up the trays, and bring the distillation column inoperative. In a process for separating a non-lithium hydroxide solid compound such as alkali metal chloride from a mixture containing lithium hydroxide and the non-lithium hydroxide solid compound in N-methylpyrrolidone, a method of feeding water to the system to separate the alkali metal chloride from lithium hydroxide by the utilization of difference in the solubility in water between the two components has been commonly adopted. However, the separation efficiency of this method was extremely poor, because the difference in the solubility in water between lithium hydroxide and alkali metal chloride is small. Another method which has been adopted is feeding water to the system and heating the mixture to convert the lithium hydroxide into lithium N-methylaminobutyrate which is soluble in N-methylpyrrolidone. Alkali metal chloride existing as a solid is then separated. This method has problems in that the procedure is complicated and a large quantity of water is left in the system. Further, lithium hydroxide cannot be separated efficiently if the mixture contains polyarylene sulfide oligomers and the like in addition to alkali metal chloride. The present invention has been achieved in order to solve the above problems, and has an object of providing an efficient and simple process for manufacturing polyarylene sulfide containing only a slight amount of alkali metal chloride and the like as impurities and having high quality, whereby recover and reuse of lithium is possible. Another object of the present invention is to provide a process for efficiently separating a non-lithium hydroxide solid compound such as alkali metal chloride from a mixture containing lithium hydroxide and the non-lithium hydroxide solid compound in an aprotic organic solvent. A further object of the present invention is to provide a process for recovering lithium ion from lithium chloride produced in a process for manufacturing polyarylene sulfide. SUMMARY OF THE INVENTION The above objects can be solved according to the present invention by a process for manufacturing polyarylene sulfide comprising, (a) a step of feeding hydrogen sulfide to a mixture comprising lithium hydroxide and an alkali metal chloride or an alkaline earth metal chloride and an aprotic organic solvent, and directly reacting lithium hydroxide and hydrogen sulfide, at a temperature of below 150°C and at a molar ratio of sulfur to lithium of between ½ and 2, (b) a step of separating the solid alkali metal chloride or alkaline earth metal chloride, (c) a step of adjusting the sulfur content of the reaction mixture to a sulfur/ lithium atomic ratio of 1/2 or less, (d) a step of feeding a dihaloaromatic compound which contains p-dichlorobenzene at a molar concentration of 50 % or more to effect a polycondensation reaction yielding lithium chloride as a by-product, and (e) a step of feeding an alkali metal hydroxide or an alkali earth metal hydroxide to the reaction mixture containing by-produced lithium chloride, and reacting lithium ions and hydroxy ions to recover lithium as lithium hydroxide as reaction product. According to this process, lithium hydroxide and a sulfur compound can be directly reacted by feeding the liquid or gaseous sulfur compound, hydrogen sulfide according to the invention, to a mixture containing lithium hydroxide and a non-lithium hydroxide solid compound, which is an alkali metal chloride or an alkaline earth metal chloride, in an aprotic organic solvent, such as N-methyl-2-pyrrolidone. Lithium hydroxide is solubilized by this reaction and the non-lithium hydroxide solid compound can be separated and removed efficiently. Furthermore, because the non-lithium hydroxide solid compound, which is an alkali metal chloride or alkaline earth metal chloride, can be efficiently separated, the residual amount of impurities such as alkali metals in the polyarylene sulfide resins obtained by the polymerization of a dichloro aromatic compound can be reduced. Thus, polyarylene sulfide resins possessing excellent electrical characteristics can be obtained. Problems such as corrosion of molding dies due to residual alkali metals can be also eliminated. In addition, lithium ion can be recovered for reuse. The process is thus simple and efficient. The above object of separating a non-lithium hydroxide solid compound from a mixture comprising lithium hydroxide and the non-lithium hydroxide solid compound in N-methylpyrrolidone can be solved according to the present invention by feeding a liquid or gaseous sulfur compound to said mixture. The non-lithium hydroxide solid compound can be efficiently separated and removed by this process. The above object of recovering lithium ion from a reaction mixture of polyarylene sulfide which contains lithium chloride can be solved according to the present invention by feeding an alkali metal hydroxide or an alkaline earth metal hydroxide to said reaction mixture of polyarylene sulfide containing lithium chloride, reacting lithium ion and hydroxy ion, and recovering the lithium ion as lithium hydroxide which is the reaction product. Lithium ion can be efficiently recovered from the lithium chloride contained in the reaction mixture of polyarylene sulfide by this process. These and other objects, features, and advantages of the present invention will become more apparent from the following description of the preferred embodiments. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a drawing schematically illustrating the process for manufacturing polyarylene sulfide of the present invention. DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS (I) Process for manufacturing polyarylene sulfide Each step of the process for manufacturing polyarylene sulfide of the present invention will be specifically illustrated. 1. Feeding of a sulfur compound (step (a)) In the present invention, a liquid or gaseous sulfur compound is first fed to, for example hydrogen sulfide is bubbled into, a mixture comprising lithium hydroxide and a non-lithium hydroxide solid compound, which is an alkali metal chloride or alkaline earth metal chloride, in an aprotic organic solvent such as N-methyl-2-pyrrolidone, to react lithium hydroxide directly with the sulfur compound. As the aprotic organic solvent, a common aprotic polar organic solvent, such as an amide compound, a lactam compound, a urea compound, an organic sulfur compound, or a cyclic organic phosphorus compound, can be preferably used either alone or in admixture. Given as examples of the amide compound among the aprotic polar organic solvents are N,N-dimethylformamide, N,N-diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dipropylacetamide, and N,N-dimethylbenzamide. Examples of the lactam compound include N-alkyl caprolactams, such as caprolactam, N-methylcaprolactam, N-ethylcaprolactam, N-isopropylcaprolactam, N-isobutylcaprolactam, N-n-propylcaprolactam, N-n-butylcaprolactam, and N-cyclohexylcaprolactam; N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone, N-isopropyl-2-pyrrolidone, N-isobutyl-2-pyrrolidone, N-n-propyl-2-pyrrolidone, N-n-butyl-2-pyrrolidone, N-cyclohexyl-2-pyrrolidone, N-methyl-3-methyl-2-pyrrolidone, N-ethyl-3-methyl-2-pyrrolidone, N-methyl-3,4,5-trimethyl-2-pyrrolidone, N-methyl-2-piperidone, N-ethyl-2-piperidone, N-isopropyl-2-piperidone, N-methyl-6-methyl-2-piperidone, N-methyl-3-ethyl-2-piperidone, and the like. Given as examples of the urea compound are tetramethyl urea, N,N'-dimethylethylene urea, and N,N'-dimethylpropylene urea. Included in examples of the sulfur compound are dimethylsulfoxide, diethylsulfoxide, diphenylsulfone, 1-methyl-1-oxosulforane, and l-ethyl-1-oxosulforane, 1-phenyl-1-oxosulforane; of the cyclic organic phosphorus. compound are 1-methyl-1-oxophosphorane, 1-n-propyl-1-oxophosphorane, and 1-phenyl-1-oxophosphorane. These aprotic polar organic solvents can be used either alone or in admixture of two or more of them. Further, it is possible to use these aprotic polar organic solvents in admixture with other solvents which do not affect the object of the present invention. Of these aprotic polar organic solvents, N-alkyl caprolactams and N-alkyl-2-pyrrolidone are preferred, with a particularly preferred solvent being N-methyl-2-pyrrolidone. The non-lithium hydroxide solid compound used in the present invention means an alkali metal chloride or an alkaline earth metal chloride. Included in the separated non-lithium hydroxide solid compounds are solid matters which do not contain lithium hydroxide at all and those containing a slight amount of lithium hydroxide. Polyarylene sulfide oligomers can be given as specific examples of such non-lithium hydroxide solid compounds other than the alkali metal chloride or alkaline earth metal chloride. Examples of the alkali metal chloride or alkaline earth metal chloride include, but not limited to, sodium chloride, potassium chloride, magnesium chloride, and barium chloride. The temperature at which the liquid or gaseous sulfur compound is fed is lower than 150°C, and more preferably lower than 130°C. If the temperature is 150°C or higher, solid sulfides may be produced and it may be difficult to separate only non-lithium hydroxide solid compounds. The amount of the liquid or gaseous sulfur compound to be fed is in the range of 1/2 to 2 mols, as sulfur, per lithium hydroxide. If this amount is less than 1/2 mol, a portion of lithium hydroxide may remain as solid and may not completely be separated from the non-lithium hydroxide solid compounds. The recovery efficiency of lithium will be poor. If the amount of the sulfur is more than 2 mols per lithium hydroxide, the reaction reaches saturation and the excess amount of the liquid or gaseous sulfur compound will be lost. In addition, feeding of an excess amount should be avoided, because liquid or gaseous sulfur compounds are noxious in many cases. Hydrogen sulfide is used as the liquid or gaseous sulfur compound in the present invention. The hydrogen sulfide may be bubbled either at normal pressure or under pressure. Although there are no specific limitations to the period of time for which the hydrogen sulfide is bubbled, normally a period of about 10-180 minutes is preferable. There are no specific limitations also to the feed rate, with a preferred range being about 10-1000 cc/min. There are also no specific limitations to the method by which the hydrogen sulfide is bubbled. It is possible to use commonly employed methods, for example to bubble gaseous hydrogen sulfide into a mixture containing lithium hydroxide and alkali metal chloride or alkaline earth metal chloride in N-methyl-2-pyrrolidone, in a 500 ml separable flask made of glass while stirring at 300-700 rpm using a disk turbine blade as a stirrer. In this instance water may be present in the mixture. 2. Separation of non-lithium hydroxide solid compound (step (b)) Lithium hydroxide which has been present as a solid in the system is dissolved in the liquid layer by feeding a liquid or gaseous sulfur compound in this manner, leaving in the system only non-lithium hydroxide solid compounds as solid components. For separating the non-lithium hydroxide solid compounds meaning an alkali metal chloride or alkaline earth metal chloride, remained in the mixture, a commonly known method such as filtration using glass filter G4 or centrifuge can be employed. The filtration may be carried out under reduced pressure. A temperature in the range of 20-150°C is usually preferable for the separation, although there are no specific limitations. 3. Adjustment of sulfur content (step (c)) In this step, the sulfur content in the reaction mixture obtained in the step (b) is adjusted by a desulfurization procedure, for example, a hydrogen sulfide removing procedure. In order to carry out the reaction of dichloro aromatic compound hereinafter described, the sulfur/lithium ratio (atomic molar ratio) is reduced to less than 1/2, and more desirably the sulfur/lithium ratio is controlled at 1/2. If this ratio is larger than 1/2, it is difficult to produce polyarylene sulfide because the reaction is difficult to proceed. There are no specific restrictions to the method of control. For example, it is possible to adjust the total sulfur content in the system by removing the sulfur compound hydrogen sulfide, bubbled for separating the alkali metal chloride or alkaline earth metal chloride by bubbling nitrogen to the liquid portion of the system after the removal of the alkali metal chloride or alkaline earth metal chloride. In this instance, the mixture may be heated. It is also possible to control the sulfur/lithium ratio by adding a lithium compound such as lithium hydroxide and lithium N-methylaminobutyrate (LMAB). 4. Polycondensation, post-treatment (step (d)) After separating the alkali metal chloride or alkaline earth metal chloride, a dichloro aromatic compound is charged and reacted to produce polyarylene sulfide. There are no specific limitations to the dichloro aromatic compound used in the present invention. A feed containing p-dichlorobenzene at a molar concentration of 50% or more is used. A one l autoclave (equipped with a paddle blade, 300-700 rpm) made of stainless steel, for example, can be used preferably as a reaction vessel. A reaction temperature of 220-260°C is applied preferably to the reaction, with a preferable reaction time being in the range of 1-6 hours. The molar ratio of the dichloro aromatic compound and sulfur existing in the system is preferably 0.9-1.2, and more preferably 0.95-1.05. A commonly used method of the post-treatment is applicable. For example, the precipitated product obtained after cooling is separated by centrifuge or filtration, and the polymer obtained is purified by repeated washing with an organic solvent, water, or the like under heating or at room temperature. The washing of the polymer may be carried out in the solid state. Alternatively, a so-called melt-washing can be applied to the polymer in the state of liquid. 5. Recovery of lithium ion (production of LiOH, step (e)) In order to collect lithium ion contained as LiCl in the polyarylene sulfide reaction mixture, an alkali metal hydroxide or alkaline earth metal hydroxide, for example, sodium hydroxide, potassium hydroxide, or magnesium hydroxide, is charged to the mixture. Of these, sodium hydroxide is preferred. The amount of the alkali metal hydroxide or alkaline earth metal hydroxide to be charged is such that the hydroxy group contained therein is 0.90-1.1 mol, preferably 0.95-1.05 mol, per 1 mol of lithium ion. If this amount is more than 1.1 mol, the purity of polyarylene sulfide is decreased depending on the succeeding procedure. If this amount is smaller than 0.90 mol, some amount of lithium is lost. In this instance, although there are no specific limitations, the reaction temperature is usually from room temperature to 230°C, preferably 65-150°C, when the alkali metal hydroxide or alkaline earth metal hydroxide is charged as an aqueous solution. If it is charged as a solid, the reaction temperature is usually 60-230°C, and preferably 90-150°C. In the case where the reaction temperature is low, the solubility is low and the reaction is retarded. If the reaction temperature is high, e.g., higher than the boiling point of NMP, the reaction must be carried out under pressure, and is thus industrially disadvantageous. There are no specific limitations to the reaction time. (II) Process for manufacturing polyarylene sulfide Each step of the process for manufacturing polyarylene sulfide (II) of the present invention will be specifically illustrated. 1. A step of feeding of a liquid or gaseous sulfur compound to the system where a non-protonic organic solvent and lithium hydroxide (LiOH) are present (a). (1) The aprotic organic solvent The solvents given in the description of said process (I) can be used as the aprotic organic solvent used in this step. (2) Preparation of a system where LiOH is present The system where an aprotic organic solvent, lithium hydroxide (LiOH) is present means the system obtained by feeding sodium hydroxide (NaOH) to a system where lithium chloride (LiCl) and an aprotic organic solvent are present or a system where lithium chloride, an aprotic organic solvent, and water are present. The method for preparing this system is specifically described. In order to collect lithium ion contained as LiCl in the reaction mixture, an alkali metal hydroxide or alkaline earth metal hydroxide, for example, sodium hydroxide, potassium hydroxide, or magnesium hydroxide, is charged to the mixture. Of these, sodium hydroxide is preferred. The amount of the alkali metal hydroxide or alkaline earth metal hydroxide to be charged is such that the hydroxy group contained therein is 0.90-1.1 mol, preferably 0.95-1.05 mol, per 1 mol of lithium ion. If this amount is more than 1.1 mol, the purity of polyarylene sulfide is decreased depending on the succeeding procedure. If this amount is smaller than 0.90 mol, some amount of lithium is lost. In this instance, although there are no specific limitations, the reaction temperature is usually from room temperature to 230°C, preferably 65-150°C, when the alkali metal hydroxide or alkaline earth metal hydroxide is charged as an aqueous solution. If it is charged as a solid, the reaction temperature is usually 60-230°C, and preferably 90-150°C. In the case where the reaction temperature is low, the solubility is low and the reaction is retarded. If the reaction temperature is high, e.g., higher than the boiling point of NMP, the reaction must be carried out under pressure, and is thus industrially disadvantageous. There are no specific limitations to the reaction time. (3) Feeding of a liquid or gaseous sulfur The methods described for step (a) and step (b) are applicable to the feeding of the liquid or gaseous sulfur in this process. 2. Dehydration step (b) There are no specific limitations as to the dehydration procedure used in the present invention. The following procedure is given as an example. (1) Temperature The temperature is determined depending on the vapor-liquid equilibrium of NMP and water. Usually, 130-205°C is preferable, but a temperature lower than 130°C is acceptable if nitrogen (N 2 ) is bubbled at the same time. An even lower temperature is possible if the dehydration is carried out under reduced pressure. (2) Allowable range of the water content Moles of water equivalent to absorbed hydrogen sulfide is generated. It is desirable to dehydrate to a degree as much as possible in order to produce high polymeric polyarylene sulfide. (3) Timing Dehydration can be carried out at any time before feeding p-dichlorobenzene (PDCB). Dehydration at the time of the hydrogen sulfide bubbling procedure is preferable in view of reducing the number of apparatus needed for the unit operation and the like. 3. A step of polycondensation by feeding dihaloaromatic compound (c) The methods described for step (c) and step (d) are applicable to the polycondensation in this process. (III) Separation of the non-lithium hydroxide solid compounds The method of step (b) and step (c) in the above-described Process can be used as the method for separating the non-lithium hydroxide solid compounds (III). (IV) Process for recovering lithium ion The process for recovering lithium ion (IV) of the present invention will be specifically illustrated. 1. A polyarylene sulfide reaction mixture containing lithium chloride There are no limitations as to the polyarylene sulfide reaction mixture used in Process (IV) for recovering lithium ion of the present invention. Polyarylene sulfide produced by any process is applicable, inasmuch as the same contains lithium chloride. The term "polyarylene sulfide reaction mixture" as used in the present invention means any reaction mixture obtained after separation of polyarylene sulfide from a mixture obtained by the reaction for forming polyarylene sulfide. The method of separation may be any commonly used separation method (e.g., solid-liquid separation, liquid-liquid separation). 2. Alkali metal hydroxide or alkaline earth metal hydroxide There are no specific limitations as to the alkali metal hydroxide or alkaline earth metal hydroxide used in this Process (IV). The examples which can be given are sodium hydroxide, potassium hydroxide, and magnesium hydroxide. Of these, sodium hydroxide which is a commercially available inexpensive industrial product is preferred. 3. Method of feeding the alkali metal hydroxide or alkaline earth metal hydroxide There are no specific limitations as to the method of feeding the alkali metal hydroxide or alkaline earth metal hydroxide used in this Process (IV). A commonly used industrial method, for example, blending the alkali metal hydroxide or alkaline earth metal hydroxide in a state of aqueous solution or solid in a tank or line, is applicable. The amount of the alkali metal hydroxide or alkaline earth metal hydroxide to be charged is such that the hydroxy ion contained therein is 0.90-1.1 mol, preferably 0.95-1.05 mol, per 1 mol of lithium ion. If this amount is more than 1.1 mol, the unit consumption of the alkali metal or alkaline earth metal hydroxide may increase and the purity of polyarylene sulfide may be decreased depending on the succeeding procedure, although there are no adverse effects on the production of lithium hydroxide. If this amount is smaller than 0.90 mol, some lithium may remain as dissolved as the chloride, leading to loss of lithium. 4. Reaction conditions of lithium ion and hydroxide ion Although there are no specific limitations to the conditions under which lithium ion and hydroxide ion are reacted, the reaction temperature is usually 0-230°C, preferably 65-150°C, when the alkali metal hydroxide or alkaline earth metal hydroxide is charged as an aqueous solution. If it is charged as a solid, the reaction temperature is usually 60-230°C, and preferably 90-150°C. In the case where the reaction temperature is low, the solubility is low and the reaction is unduly retarded. If the reaction temperature is high, e.g., higher than the boiling point of NMP, the reaction must be carried out under pressure, and is thus industrially disadvantageous. There are no specific limitations to the reaction time. 5. Recovery of lithium ion Although it is possible to recover lithium ion as solid lithium hydroxide, recovering it as a lithium hydroxide solution for feeding to the next step is more desirable for continuously producing polyarylene sulfide. That is to say, if a liquid or gaseous sulfur compound is fed to an aprotic organic solvent containing solid lithium hydroxide, alkali metal chloride or alkaline earth metal chloride, lithium hydroxide becomes soluble in the aprotic organic solvent, thus enabling the alkali metal chloride or alkaline earth metal chloride which is insoluble in the solvent to be separated or removed by solid-liquid separation. The mother liquor is then sent to the next'step of the process for manufacturing polyarylene sulfide as is. Japanese Patent Applications No. 343634/1993 filed on December 16, 1993, No. 012215/1994 filed on January 10, 1994, 044892/1994 filed on February 18, 1994, and No. 076646/1994 filed on March 23, 1994 are herein incorporated as a reference. Other features of the invention will become apparent in the course of the following description of the exemplary embodiments which are given for illustration of the invention and are not intended to be limiting thereof. EXAMPLES Example 1 (1) Hydrogen sulfide bubbling step 415.94 g (4.2 mol) of N-methyl-2-pyrrolidone, 123.5 g of a mixture of LiOH and NaCl (1.5 mol each), and 27.0 g (1.5 mol) of deionized water were placed in a 500 ml separable flask equipped with a stirring blade. The mixture was heated to 130°C, whereupon hydrogen sulfide was bubbled at a rate of 700 ml/min for 35 minutes, while controlling the temperature at 130°C all the time. The feeding of hydrogen sulfide was terminated and sulfur was quantitatively analyzed to find that the quantity absorbed was 0.975 mol. The molar ratio S:Li was thus found to be 0.65. The iodometric method using iodine and sodium thiosulfate (a method of adding a diluted hydrochloric acid solution to the sample and further adding a surplus amount of an iodine solution, and then measuring an excess amount of iodine solution using a sodium thiosulfate standard solution by reverse titration) was used for the quantitative analysis of the sulfur in the mixture. (2) NaCl separation step The solution in which hydrogen sulfide was absorbed was filtered under reduced pressure through glass filter which was warmed at 130°C. The residue on the filter was washed with a large quantity of N-methyl-2-pyrrolidone at 130°C and dried at 150°C under reduced pressure to obtain 87.4 g of a solid dry product. The results of X ray diffractiometry revealed that the spectrum of this product was the same as that of NaCl, with no spectrum of LiOH. The above results demonstrated that bubbling of hydrogen sulfide to a mixture of LiOH and NaCl effected the reaction only of LiOH and synthesized a complex which is soluble in N-methyl-2-pyrrolidone, thereby enabling NaCl to be separated. (3) Sulfur content adjustment step On the other hand, 400.0 g of the filtrate in which hydrogen sulfide was absorbed were transferred to a separable flask with the same volume as that used above and heated to 150°C, whereupon N 2 was bubbled at a rate of 700 ml/min until the ratio of S:Li became 0.50, thereby removing excessively absorbed hydrogen sulfide. The ratio of S:Li = 0.50 was reached in 70 minutes while bubbling N 2 . (4) Polycondensation - post-treatment step The liquid obtained above was transferred to a 1 l stainless steel autoclave. 173.0 g of p-dichlorobenzene (POCB) were added to make the molar ratio PDCP:S 1.00, and the mixture was heated to 240°C, at which temperature the pre-condensation was carried out for 30 minutes. The temperature was then raised to 260°C and the polymerization was carried out for 3 hours. After cooling, granules of polymer obtained were washed with purified water, replaced with acetone, and dried in a vacuum dryer. The weight of the polymer was 119.5 g and the inherent viscosity (ηinh), an index of the molecular weight, was 0.34. (5) LiOH production step 415.94 g (4.2 mol) of N-methyl-2-pyrrolidone and 63.585 g (1.5 mol) of lithium chloride were charged in a 500 ml separable flask made of glass and equipped with a stirring blade, and lithium chloride was dissolved at 90°C. After dissolution, 125.0 g of 48 wt% sodium hydroxide solution (corresponding to 1.5 mol of MaOH) were added. A white solid was produced instantaneously by the addition of sodium hydroxide. Water was removed while raising the temperature in a nitrogen stream. After cooling, the dehydrated mixture was filtered through a glass filter (G4) under reduced pressure at room temperature. The residue on the filter was dried under reduced pressure at 150°C and weighed to find that 123.5 g of the product were obtained. The molar ratio of Na:Li:Cl was confirmed to be 1.03:1.00:1.00 as a result of elementary analysis. The results of X ray diffractiometry revealed that the spectra were identical with NaCl and LiOH. Further, no lithium ion and sodium ion were detected in the supernatant (NMP layer) by the ion chromatogram. Based on these results, LiCl and NaOH were confirmed to have been converted to LiOH. and NaCl at a yield of almost 100%. Example 2 415.94 g (4.2 mol) of N-methyl-2-pyrrolidone and 63.585 (1.5 nol) of lithium chloride were charged in a 500 ml separable flask made of glass and equipped with a stirring blade, and lithium chloride was dissolved at 90°C. After dissolution, 125.0 g of 48 wt% sodium hydroxide solution (corresponding to 1.5 mol of NaOH) were added. A white solid was produced instantaneously by the addition of sodium hydroxide. Water was removed while raising the temperature in a nitrogen stream. After cooling, the dehydrated mixture was filtered through a glass filter (G4) under reduced pressure at room temperature. The residue on the filter was dried under reduced pressure at 150°C and weighed to find that 123.5 g of the product were obtained. The molar ratio of Na:Li:Cl was confirmed to be 1.03:1.00:1.00 as a result of elementary analysis. The results of X ray diffractiometry revealed that the spectra were identical with NaCl and LiOH. Further, no lithium ion and sodium ion were detected by the ion chromatogram in the supernatant (NMP layer). Based on these results, LiCl and NaOH were confirmed to have been converted to LiOH and NaCl at an yield of almost 100%. Example 3 A large amount of white solid was produced by the addition of 168.3 g of 50 wt% potassium hydroxide solution (corresponding to 1.5 mol of KOH) instead of the 125.0 g of 48 wt% sodium hydroxide solution in Example 2. The same procedure was followed thereafter to obtain 146.1 g of a white precipitate. Almost no lithium ion and potassium ion were detected by the ion chromatogram in the supernatant (NMP layer). Further, the results of X ray diffractiometry revealed that the spectra were identical with KCl and LiOH. Based on these results, LiCl and KOH were confirmed to have been converted to LiOH and KCl at an yield of almost 100%. Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims: A process for manufacturing polyarylene sulfide, comprising (a) a step of feeding hydrogen sulfide to a mixture comprising lithium hydroxide and an alkali metal chloride or an alkaline earth metal chloride and an aprotic organic solvent, and directly reacting lithium hydroxide and hydrogen sulfide, at a temperature of below 150°C and at a molar ratio of sulfur to lithium of between ½ and 2 (b) a step of separating the solid alkali metal chloride or alkaline earth metal chloride, (c) a step of adjusting the sulfur content of the reaction mixture to a sulfur/lithium atomic ratio of 1/2 or less, (d) a step of feeding a dihaloaromatic compound which contains p-dichlorobenzene at a molar concentration of 50 % or more to effect a polycondensation reaction yielding lithium chloride as a by-product, and (e) a step of feeding an alkali metal hydroxide or an alkali earth metal hydroxide to the reaction mixture containing by-produced lithium chloride and reacting lithium ions and hydroxy ions to recover lithium as lithium hydroxide as reaction product The process for manufacturing polyarylene sulfide according to claim 1, wherein said aprotic organic solvent is N-methyl-2-pyrrolidone. The process for manufacturing polyarylene sulfide according to claim 1 or 2, wherein the amount of the alkali metal hydroxide or alkaline earth metal hydroxide to be added, in terms of the hydroxy ion, is 0.90-1.1 mol per 1 mol of lithium ion. The process for manufacturing polyarylene sulfide according to anyone of claims 1 to 3, wherein said alkali metal hydroxide or alkaline earth metal hydroxide is sodium hydroxide, potassium hydroxide, or magnesium hydroxide.

Inventors: KOYAMA YOSHINARI, NISHITANI HIROSHI, OGATA NORIO, KOYAMA, YOSHINARI, NISHITANI, HIROSHI, OGATA, NORIO, KOYAMA, YOSHINARI, C/O IDEMITSU PETROCHEMICAL, NISHITANI, HIROSHI, C/O IDEMITSU PETROCHEMICAL, OGATA, NORIO, C/O IDEMITSU PETROCHEMICAL
Applicants: IDEMITSU PETROCHEMICAL CO, IDEMITSU PETROCHEMICAL CO., LTD.
Application year: 1994
Main classification: C08G75
IPC codes: C01D3, C08G75